The present invention relates in general to an improvement of a limited sliding ball spline assembly, and, in particular, to the ball spline assembly capable of transmitting a large torque and obtaining a ball spline combination without any backlash.
Referring to FIG. 1, there is shown a conventional design of the limited sliding ball spline assembly. Such ball spline assembly comprises an outer sleeve 1 having a circular cross-section, the outer sleeve 1 being machined on the inside wall surface thereof to form plural parallel grooves 3, which extend substantially the entire length of the outer sleeve 1, a shaft 2 being inserted in the outer sleeve 1, the shaft being machined on the outside wall surface thereof to form plural parallel grooves 4, which extend substantially the entire length of the shaft 2, the parallel grooves 3 and 4 being opposite each other and forming plural rectilinear raceways for balls 6, and relative displacements in the rectilinear directions and transmission of torque between the outer sleeve 1 and the shaft 2 being carried through those balls 6.
However, in such conventional ball spline assembly, it is unavoidable that the distance between the inside wall surface of the outer sleeve 1 and the outside wall surface of the shaft 2 becomes relatively wide or large because there is inserted a ball retainer 5 therebetween, thus the bearing surfaces with which balls 6 contact in the raceways are very small and therefore it is not possible to transmit the large torque between the outer sleeve 1 and the shaft 2. For details, as shown in FIG. 1, the diameter of the ball retainer 5 must be smaller than the pitch diameter for setting the balls 6. When the shaft 2 rotates in the direction of the arrow A, the region in each groove 4 of the shaft 2 which contacts with the balls 6 and receives the contact pressure in the direction of rotation of the shaft 2 becomes the arc a.sub.1 b.sub.1 which is formed from the intersecting point a.sub.1, which the imaginary line between the center of the ball 6 and the center axis of the shaft 2 crosses with the groove 4, to the end point b.sub.1 of the groove 4, and this arc a.sub.1 b.sub.1 becomes smaller in consequence with the enlargement of the distance between the inside wall surface of the outer sleeve 1 and the outside wall surface of the shaft 2. Thereby it is unavoidable that the component P.sub.1 of the contact pressure P in the direction of rotation becomes small.